Posts: 1690
Joined: 3/22/2002 From: Lincoln, NE, USA Status: offline
Update on my first large composite project. Have been busy flying during the summer, so this project had been placed on hold. Now that the weather has changed, I’ve pulled two complete fuses and various spare “test” parts from the molds.
Molds were made from plug mentioned in previous thread. I used US Composites epoxy. First layer is thick epoxy made thicker with cabosil and tinted black with laser printer toner. Then 1 layer of 8oz cloth, 5 layers of epoxy mat, and finished with one layer of 8oz again. This built up a ¼” or greater mold thickness.
First fuse pulled is all glass, 3oz satin, then 6oz and 8oz in the nose, ~3/32” thick foam core in tail, and 3 oz satin on back side of foam. Second fuse is 3oz satin, 7oz Kevlar in nose, and 8oz glass in tail, foam core as before, and 3/4oz on back of foam. Weights and cloth types were mainly chosen because that is what I had on hand. All up weight before trimming is just shy of 40oz. The fuses are more than strong enough, so I believe I can drop cloth weight by about 25%. I also had issues with vacuum bagging on the fuse molds, so I know I could have pulled another couple of ounces of epoxy from the parts. With lighter cloth schedules and a vacuum bag that seals, I hope to obtain a 30oz total weight with primer.
From RCU tips, I finally made a vacuum bag that holds vacuum. I used 4mil vinyl that can be found at Menards, Home Depot, etc. Three edges were sealed with a covering iron turned to max, using paper between the iron and vinyl to prevent the vinyl melting onto the iron. This worked extremely well. To seal the 4th open end, bought two sizes of PVC water pipe, and cut a slot on the larger one. The result is they click together and seal the bag. For an inlet, I used water fittings, with home made bonded washers (fender + rubber sealing washer bonded with CA) on both sides and some silicone caulk for extra insurance. For breather cloth, I used felt underlay used for laminate flooring. For the pump, I borrowed an old refrigerator compressor. This is an eclectic mix, but I will say it works extremely well. I can pull 25” of mercury and hold it.
Once I was able to pull hard vacuum, my part weight wend down slightly, but zillions of micro pinhole showed up, I assume because I removed more epoxy. Checking RCU, I tried priming in the mold, the parts came out with basically no pinholes. I used epoxy parfilm spray mold release designed specifically for painting in the mold, an then used a PPG Omni urethane primer. It releases fine and is bonded well to the glass/epoxy. I believe you can see part of the part (canopy) in one of the pics.
I’m now in the process of making a reservoir tank and vacuum switch. Using a pipe mender/extender, which I spring loaded internally, I have a vacuum operated cylinder I intend to used to operate a simple switch for the pump. Total cost, about $6. I have an old 11 gallon compressor tank to use as the reservoir. It only takes the pump about 5 –10 minutes to pull 25+” of mercury on the tank. I unplugged the compressor and let the contraption sit over night. There should be no question the extender seals as I held 25+” inches over 12 hours with the pump unplugged.
While I’m not a stranger to making composite parts, there was a pretty steep learning curve on this project, and I thank everyone who has helped and inspired me so far. I still have a lot to learn., but I hope my reasonable success using inexpensive and common items is of benefit to others who would like to try making composites, but don’t want to foot a huge initial investment.
Posts: 62
Joined: 1/28/2005 From: , NY, USA Status: offline
THe one question i do have, and i havnt done yet myself is. doing vacuum bagging, do you need a foam, batting material? what does it do? nice work by the way =) put more details.
Posts: 1690
Joined: 3/22/2002 From: Lincoln, NE, USA Status: offline
Foam in the tail is expanded polystyrene, i.e. standard white foam you can get at any building supply store. I made a jig to cut the foam thin, basically just a 2'x3' board with some screws in it that hold the hot wire a small distance above the board. Push foam thru and presto, thin sheets of foam. I also have a template to cut the foam to the proper shape so it lays into the mold halves.
Unfortunately, it is hard to see the foam core in any of my pics. On the Kevlar fuse, you can see the start of the foam core (darker semi circle starting mid fuse.) Using a "highly precise squeeze" test, I can tell you there is a night vs day difference between foam and non-foam fuse sides. The tail with the foam is extremely stiff, while the non-foam sides wiggle a bunch. The wiggle is OK because there will be a floor installed, wing tube, tank formers, etc. that will stiffen the center fuse area.
Chelapa: I'm sure the foam isn't strictly required as there are other ways to stiffen the tail. I've mainly been copying things I know work, and since my existing 2M ship is built this way, I copied it. I will say it seems to make a huge difference is stiffness with a very small weight gain.
Posts: 62
Joined: 1/28/2005 From: , NY, USA Status: offline
Johnw , not sure you got my email. but i hope you can help me out. How did you create that nozzle going into the bag? what parts did you use, leaks?? I used a 4 mil bag last night, and wow i think i had 2-3 leaks somewhere in the bag =( not sure why.
Posts: 1690
Joined: 3/22/2002 From: Lincoln, NE, USA Status: offline
Chelapa,
The nozzle was made from parts available at any major hardware store. I purchased all my parts at the local Menards. No leaks.
My parts list include a 1/4" barb adapter (threaded on one side), an adapter of any kind that mates with the threads on the barb adapter (I selected a simple reducer), two fender washers of suitable size, and two rubber sealing washers of suitable size.
I bonded the rubber sealing washers to the fender washers, but I'm sure that isn't required. I cut a small hole, slightly oversized in the bag. I smeared some silicone on the rubber washers, and the assembled the lot, obviously with the rubber washers next to the bag, then fenders, then fittings. I tightened just to the point where the rubber washers started to curl from the pressure.
The adapter sealed before the silicon had even set. As best I can tell, I have zero loss on the adapter and I can hold 30" of mercury indefinitely in the bag.
One note: I've tried many different plastics when making bags and vinyl is the only one that seems to work well, at least for me. I had no end of problems using painters drop cloth, garbage bags, and similar. They always leaked. Vinyl worked much, much better. Vinyl is a bit harder to find than plastic drop cloths. The only place I've seen it is next to the window sealing treatments (shrink film.) It comes on rolls, and runs about $15-$20 for a 4' x 25' roll at 4mill.
One thing I learned is the smallest pinhole leak in a bag will prevent you from pulling vacuum. It is critical that the bag is sealed everywhere, no exceptions. Be sure all your edges are sealed using the iron trick (Covering iron turned to max, use paper between iron and vinyl.) Once sealed, the 4mill seems durable enough for maybe 10+ sessions. I've pumped mine down about 10 times, and it still holds vacuum, but I have punched a few leaks due to my mold shapes. Easy fix, just cut a patch of vinyl, and iron it on over the hole.
Hope that helps.
EDIT: I was also going to mention I used peel-ply and paper towels to suck epoxy out of the layup. For peel-ply, I went tot he local fabric store and purchased nylon cloth typically used for jacket linings. After layup, put the nylon cloth down, then some paper towels. Put the lot into the bag and pump it down. The excess epoxy is pulled thru the peel-ply into the towels. Once cured, the peel-ply rips cleanly off the layup, taking the paper towels with it.
< Message edited by JohnW -- 10/28/2006 5:42:49 PM >
Posts: 62
Joined: 1/28/2005 From: , NY, USA Status: offline
Hey guys. So i tried a part and it didnt come out so well =(
-I didnt use a breather or peel ply. I sucked about 22"hg from the bag and it had somewhat of a leak but i let it run for about 6 hours. then i turned it off. but, while i was pulling, i noticed certain areas in the bag still had air, would wrinkle, etc. In these area's of wrinkle, there sometimes would be very little epoxy, or the fiberglass would pull away from the mold, and i had certain areas that pulled away completely. John, i see that your mold has a lot of corners, i wonder how you made the bag conform to all corners. is it b/c i had no peel ply and breather??? =( i hope im not wasting my time
Posts: 1690
Joined: 3/22/2002 From: Lincoln, NE, USA Status: offline
I'm far from a vacuum bag expert, but I'd think you must use a breather cloth, otherwise the bag could collapse and seal in pockets of air like you describe. I used pel-ply with papertowels as the last layer to collect excess epoxy. I think the paper towel and pel-ply also help to evacuate all air from the bag in the area of the mold as the paper towels act as a breather cloth. I too would have wrinkles in the bag, but under high vacuum they all fold flat. They really don't matter as long as the peel-ply is still pressing hard on the layup. Very little epoxy is generally OK as long as the cloth stays wetted out. The idea behind peel-ply and towels as I understand it is to draw out as much excess epoxy as possible. Excess epoxy is just dead weight as it doesn't add much strength alone. If your bag is pulling the glass away from the mold, which has happened to me, you just need to work more bag material into the mold area. Push in folds of bag. As it sucks down, let it wrinkle. Tthat's OK as long as everything is being pressed into the mold properly. If it looks messed up, release the vacuum and work more bag material into the mold, then suck down again, etc. Hope that helps.
Posts: 62
Joined: 1/28/2005 From: , NY, USA Status: offline
I think that last 2 sent. hit the money,. then the rest as well. I did not let enough of the bag into the mold =( and i will now use a "peel" ply but really a plastic vin. bag 1 sheet 2 mil with tons of pin holes in it. (i researched some and someone used that and it worked) along with breather =)
thanx john! i will let you know what happens with the next one.
Posts: 62
Joined: 1/28/2005 From: , NY, USA Status: offline
Hey john. With much success i got it to work. atleast the vacuum part + no leaks. NOOO leaks. it held and my air compressor never turned on! its been over 12 hours now. There were 2-3 things missing in my setup when i first started.
1. Not enough breather. i always only put it near the nozzle. but, u HAVE to have it on top of your part + a plastic sheet + connect the paper towels from the nozzle to the area where its on top of the part. so the air passes through the paper 2. a plastic sheet 2 mill with a crap load of pin holes below the paper towel and above the part to such excess epoxy out. 3. the nozzle itself needed to be sealed near the bag area. used the same stuff that i used to seal the bags and wam bam thank you mam! no leaks
i will check out how the part came out. my pieces dont have flanges, so the epoxy went below the mold, how bad is that? =\ and how can i avoid it??
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Update - First large composite project - 
